1. Field of the Invention
The present invention relates to a rotary developing device installed in a copier, printer, facsimile transceiver or similar photographic image forming apparatus which is electrostatically formed on an image carrier. More particularly, the invention is concerned with a toner supplying system suitable for use in the rotary developing device which has a plurality of rotary developing units.
2. Description of the Related Art
Recently, there has been a requirement for copying machines which can perform copying of both black-and-white images and a color images in accordance with the color of documents.
In a color electrophotographic copier, for example, a latent image carrier charged in a predetermined polarity is exposed by light rays. Electrostatic latent images reproduced in different color are thus formed on the latent image carrier. The respective electrostatic latent images are developed by toners of different colors. Each toner image is transferred to the same transfer sheet so as to obtain a color image.
In a full color electrophotographic copier, for example, respective color electrostatic latent images are formed on a latent image carrier by the exposure of color-resolved light. The respective color electrostatic latent images are each developed by a toner having a color complementary to the color-resolved light. These toner images are transferred onto the same transfer sheet so as to obtain a multiple-color image. Toner images for the different colors may also be duplicated onto respective different transfer sheets so as to obtain mono-color images.
In the above stated image forming apparatus, it is necessary that respective electrostatic latent images formed on the latent image carrier are developed by respective toners of different colors.
A rotary developing device for an image forming apparatus and used to develop the electrostatic latent images is commonly known. In the rotary developing device, there are a plurality of rotary developing units for developing or visualizing the electrostatic latent images with respective toner for different colors. The plurality of rotary developing units is rotatably supported around a common rotational axis. Respective rotary developing units of the plurality of rotary developing units are selectively moved to a developing position facing to the latent image carrier. Respective electrostatic latent images on the latent image carrier are developed by respective toner for different colors to produce images.
Toner is consumed during the process and it is necessary to supply toner to the respective rotary developing units. The following method for supplying toner to the rotary developing units is commonly known:
A toner cartridge which is a container for toner is fixedly arranged in a corresponding rotary developing unit, and is separated from the rotary developing unit. Respective rotary developing units are each connected to the toner cartridges by a resilient cylinder. A toner conveying member in the form of a screw is formed in each resilient cylinder. The toner conveying member is rotated so as to supply toner from the respective toner cartridge to the corresponding rotary developing unit.
Another method for supplying a toner to the rotary developing units is also commonly known as follows:
Toner cartridges are rotatably supported in the plurality of rotary developing units, and are unitary with the rotary developing units. Respective rotary developing units are connected to the toner cartridges by a separate toner conveying member. The toner conveying member is rotated so as to supply a toner from each respective toner cartridge to the corresponding rotary developing unit.
However, in the conventional method for supplying the toner to the rotary developing units, the toner in each toner cartridge is conveyed and supplied to the respective rotary developing unit by the toner conveying member. It is thus necessary to provide the toner conveying member and a driving member for driving the toner conveying member. The rotary developing apparatus is thus large, complex and expensive. Moreover, when the toner is conveyed by the toner conveying member, the toner is subjected to large mechanical forces and is rapidly deteriorated thereby.